In the prior art there has always been a need for telephone line sharing apparatus that permits a device to share a telephone line of a key telephone system or PBX instead of installing a separate line for such a device. This has been most desireable for small businesses that only have a few telephone sets, but do not want to have more than one telephone line and that do not want the cost of installing a small key system or PBX. To accomplish this end for small businesses, typically a manually operated key or switch apparatus is provided. When it is desired to provide exclusive access to a shared telephone line for a device, a key or switch is operated and such access is had. This access may be had whether originating or receiving a call. When the call is completed the key or switch connected to the device must be released. Problems arise, however, when someone forgets to release the lockout key after completing a call. Others wishing to gain access to the shared telephone line must find the unreleased lockout key or switch before being able to place a call.
The need for exclusive access to a telephone line has become more important in this day of computers, facsimile machines and point of sale machines (credit card machines). The computers are typically small computers known as personal computers and are widely used. They are connected to the telephone line via a modem for called up access to another computer also equipped with a modem. When a computer is connected to a line via a modem and data is being transmitted over the telephone line between the computers, any disturbance on the telephone line can damage the transmitted data and thereby make it unusable. Retransmission of the data is then required. Such disturbances are often caused by a call waiting tone on the telephone line, and by another telephone set or device connected to the shared line being taken off hook while data transmission is taking place. A more dangerous problem is thereby created because the transmitted data or programs being sent or received over the telephone line are damaged without knowledge of the damage, and the damage is not discovered until the damaged data or programs are used and cause further problems. This problem has been partially solved in that the telephone companies now provide the ability to temporarily disable the call waiting feature by keying certain digits prior to originating a call. This is called "selective call waiting" and the call waiting feature is temporarily disabled for a single call, and is automatically reenabled thereafter. Disabling the "call waiting" feature for a telephone call is typically done by keying *70 on a touch tone dial telephone set, or by keying 1170 on a rotary dial telephone set prior to dialing a telephone number. The selective call waiting may also be used with a three way call feature provided by the telephone company.
However, the problem of interrupting a data call between computers by inadvertently taking another telephone set or communication device off hook still exists. The transmitted data or programs are still damaged. The only solution has been the manual key lockout equipment which causes other problems as described above.
Thus, there is a need in the art for lockout apparatus that can automatically provide exclusive, private access to a shared telephone line, and which will automatically restore shared access to the telephone line when a call is terminated.